An automatic titration setup for the chemiluminometric determination of the copper complexation capacity in opaque solutions.

An automatic titration setup exploiting flow analysis was proposed for the evaluation of the copper complexation capacity of highly opaque substances (milk and humic substances). The binary search approach was implemented in a flow-batch analyzer, in order to add the in-line selected titrant (e.g. copper ions) volumes to the sample. When the titration end-point was surpassed, the free metal ions catalyzed the reaction of luminol with hydrogen peroxide, yielding the chemiluminescence, which was quantified even in solutions of high opacity. Accuracy was assessed through addition/recovery tests involving classical complexing species (EDTA, DTPA and DTTC), and recoveries ranged from 96% to 115%. The proposed system requires low amounts of reagents and samples (0.42 mg of luminol, 82 µg H2O2, 1.10 mL of sample) per titration run, meaning ca. 12 mL of effluent per titration, and yields precise results (5% r.s.d.) at a sampling throughput of 43 h-1.

Automatic multicommuted flow-batch setup for photometric determination of mercury in drinking water at ppb level.

Herein, a multicommuted flow-batch setup and a photometric procedure for the determination of mercury at the ppb level in aqueous samples are described. The setup was designed to implement a versatile solvent extraction and pre-concentration strategy by combining flow-batch and multicommuted flow analysis approaches. The photometric method was based on Hg(II) reaction with dithizone in a chloroform medium, which was also used as the extracting organic solvent. The flow analysis system was composed of a homemade syringe pump module, a set of solenoid valves, two Aquarius mini-pumps, and a flow-batch chamber. The homemade photometer was comprised of a light emitting diode (LED), photodiode, and homemade flow cell (50 mm length). The flow system and photometer were controlled using an Arduino Due board, running custom-written software. After optimizing the operational conditions, the effectiveness of the developed system was evaluated for the determination of the mercury concentration in drinking water. For accuracy assessment, samples were analyzed using a spiking methodology and an independent method, yielding a recovery ranging from 92% to 108%. Other important characteristics of the proposed method were found as follows: linear response range, 0.5-10.0 µg L-1 (r = 0.9984); limit of detection 0.38 µg L-1 Hg(II); consumption of dithizone and chloroform, 1.85 µg L-1 and 0.8 mL per analysis, respectively; coefficient of variation, 2% (n = 10); sampling throughput, 20 determinations per h.

Photogeneration of silver nanoparticles induced by UV radiation and their use as a sensor for the determination of chloride in fuel ethanol using a flow-batch system.

Photogeneration of silver chloride nanoparticles (AgCl-NPs) in fuel ethanol was used as a sensor for the spectrophotometric determination of chloride. A low-power UV radiation source (germicidal lamp) was placed close to a flow-batch chamber and a 3D-built support for the reaction chamber was used to couple fiber optic cables in the orthogonal direction with the UV-lamp beam, allowing the monitoring of nanoparticle formation in real-time using a spectrophotometer. The nanoparticles were characterized via high-resolution transmission electron microscopy, energy-dispersive X-ray spectroscopy, and UV-vis spectroscopy. Most of the particles exhibited a spherical shape with an average diameter of 18 nm. The absorbance maximum was observed at 440 nm and was used for chloride determination in fuel ethanol. Under the optimized working conditions, the system exhibited a linear response from 0.05 to 0.8 mg L-1 chloride, with a limit of detection (95%) and coefficient of variation (n = 8) were estimated to be 12 µg L-1 chloride and 2.2%, respectively. The intra- and inter-day precisions (coefficient of variation) were 2.4% and 2.8%, respectively. This working range (0.05-0.8 mg L-1) for the determination of chloride at low concentrations met the limit required by Brazilian legislation (limit of 1.0 mg kg-1). Analyses of fuel ethanol were performed without sample treatment and the obtained results were compared with those obtained by ion-chromatography. No significant differences were observed between the two methods at the 95% confidence level.

A Sensitive Photometric Procedure for Cobalt Determination in Water Employing a Compact Multicommuted Flow Analysis System.

In this work, a multicommuted flow analysis procedure is proposed for the spectrophotometric determination of cobalt in fresh water, employing an instrument setup of downsized dimension and improved cost-effectiveness. The method is based on the catalytic effect of Co(II) on the Tiron oxidation by hydrogen peroxide in alkaline medium, forming a complex that absorbs radiation at 425 nm. The photometric detection was accomplished using a homemade light-emitting-diode (LED)-based photometer designed to use a flow cell with an optical path-length of 100 mm to improve sensitivity. After selecting adequate values for the flow system variables, adherence to the Beer-Lambert-Bouguer law was observed for standard solution concentrations in the range of 0.13-1.5 µg L-1 Co(II). Other useful features including a relative standard deviation of 2.0% (n = 11) for a sample with 0.49 µg L-1 Co(II), a detection limit of 0.06 µg L-1 Co(II) (n = 20), an analytical frequency of 42 sample determinations per hour, and waste generation of 1.5 mL per determination were achieved.

A Highly Sensitive Multicommuted Flow Analysis Procedure for Photometric Determination of Molybdenum in Plant Materials without a Solvent Extraction Step.

A highly sensitive analytical procedure for photometric determination of molybdenum in plant materials was developed and validated. This procedure is based on the reaction of Mo(V) with thiocyanate ions (SCN-) in acidic medium to form a compound that can be monitored at 474 nm and was implemented employing a multicommuted flow analysis setup. Photometric detection was performed using an LED-based photometer coupled to a flow cell with a long optical path length (200 mm) to achieve high sensitivity, allowing Mo(V) determination at a level of µg L-1 without the use of an organic solvent extraction step. After optimization of operational conditions, samples of digested plant materials were analyzed employing the proposed procedure. The accuracy was assessed by comparing the obtained results with those of a reference method, with an agreement observed at 95% confidence level. In addition, a detection limit of 9.1 µg L-1, a linear response (r = 0.9969) over the concentration range of 50-500 µg L-1, generation of only 3.75 mL of waste per determination, and a sampling rate of 51 determinations per hour were achieved.

A clean photometric method for the determination of losartan potassium in pharmaceuticals exploiting light scattering effect and employing a multicommuted flow analysis approach.

This paper describes an environmentally friendly procedure for the determination of losartan potassium (Los-K) in pharmaceuticals. The photometric method was based on the light scattering effect due to particles suspension, which were formed by the reaction of Los-K with Cu (II) ions. The method was automated employing a multicommuted flow analysis approach, implemented using solenoid mini-pumps for fluid propelling and a homemade LED based photometer. Under the optimized experimental conditions, the procedure showed a linear relationship in the concentration range of 23.2-417.6mgL-1 (r=0.9997, n=6), a relative standard deviation of 1.61% (n=10), a limit of detection (3.3*σ) estimated to be 12.1mgL-1, and a sampling rate of 140 determinations per hour. Each determination consumed 12µg of copper (II) acetate and generated 0.54mL of waste.

Development of a new procedure for the determination of captopril in pharmaceutical formulations employing chemiluminescence and a multicommuted flow analysis approach.

This paper describes a new technique for the determination of captopril in pharmaceutical formulations, implemented by employing multicommuted flow analysis. The analytical procedure was based on the reaction between hypochlorite and captopril. The remaining hypochlorite oxidized luminol that generated electromagnetic radiation detected using a homemade luminometer. To the best of our knowledge, this is the first time that this reaction has been exploited for the determination of captopril in pharmaceutical products, offering a clean analytical procedure with minimal reagent usage. The effectiveness of the proposed procedure was confirmed by analyzing a set of pharmaceutical formulations. Application of the paired t-test showed that there was no significant difference between the data sets at a 95% confidence level. The useful features of the new analytical procedure included a linear response for captopril concentrations in the range 20.0-150.0 µmol/L (r = 0.997), a limit of detection (3σ) of 2.0 µmol/L, a sample throughput of 164 determinations per hour, reagent consumption of 9 µg luminol and 42 µg hypochlorite per determination and generation of 0.63 mL of waste. A relative standard deviation of 1% (n = 6) for a standard solution containing 80 µmol/L captopril was also obtained.

An air carrier flow system for the spectrophotometric determination of water in biodiesel exploiting bleaching of the cobalt chloride complex.

Water content is an important parameter in biodiesel quality control, as excess of this substance may lead to biofuel hydrolysis, microorganism proliferation, and alterations in the oxidative stability of the biofuel. The threshold limit is established as 200 mg kg(-1) and the determination is usually based on Karl Fischer titration. In this work, a simple, reliable and environmentally friendly procedure is proposed for water determination in biodiesel by exploiting a multicommuted flow system with air carrier stream. The method relies on the color fading of the cobalt chlorocomplex in the presence of the analyte, which is monitored by spectrophotometry. A linear response was observed from 100 to 5000 mg kg(-1) water, with detection limit, coefficient of variation (n=20) and sampling rate estimated as 25 mg kg(-1), 0.7% and 30 h(-1), respectively. The procedure consumes only 3.5 µg of CoCl2 and generates 750 µL of waste per determination. Results obtained by using the standard additions method agreed with those attained by the Karl Fischer titration at the 95% confidence level.

Green chemistry and the evolution of flow analysis. A review.

Flow analysis has achieved its majority as a well-established tool to solve analytical problems. Evolution of flow-based approaches has been analyzed by diverse points of view, including historical aspects, the commutation concept and the impact on analytical methodologies. In this overview, the evolution of flow analysis towards green analytical chemistry is demonstrated by comparing classical procedures implemented with different flow approaches. The potential to minimize reagent consumption and waste generation and the ability to implement processes unreliable in batch to replace toxic chemicals are also emphasized. Successful applications of greener approaches in flow analysis are also discussed, focusing on the last 10 years.

An environmental friendly procedure for photometric determination of hypochlorite in tap water employing a miniaturized multicommuted flow analysis setup.

A photometric procedure for the determination of ClO(-) in tap water employing a miniaturized multicommuted flow analysis setup and an LED-based photometer is described. The analytical procedure was implemented using leucocrystal violet (LCV; 4,4',4''-methylidynetris (N,N-dimethylaniline), C(25)H(31)N(3)) as a chromogenic reagent. Solenoid micropumps employed for solutions propelling were assembled together with the photometer in order to compose a compact unit of small dimensions. After control variables optimization, the system was applied for the determination of ClO(-) in samples of tap water, and aiming accuracy assessment samples were also analyzed using an independent method. Applying the paired t-test between results obtained using both methods, no significant difference at the 95% confidence level was observed. Other useful features include low reagent consumption, 2.4 µg of LCV per determination, a linear response ranging from 0.02 up to 2.0 mg L(-1) ClO(-), a relative standard deviation of 1.0% (n = 11) for samples containing 0.2 mg L(-1) ClO(-), a detection limit of 6.0 µg L(-1) ClO(-), a sampling throughput of 84 determinations per hour, and a waste generation of 432 µL per determination.

Downscaling a multicommuted flow injection analysis system for the photometric determination of iodate in table salt.

In this work a downscaled multicommuted flow injection analysis setup for photometric determination is described. The setup consists of a flow system module and a LED based photometer, with a total internal volume of about 170 microL. The system was tested by developing an analytical procedure for the photometric determination of iodate in table salt using N,N-diethyl-henylenediamine (DPD) as the chromogenic reagent. Accuracy was accessed by applying the paired t-test between results obtained using the proposed procedure and a reference method, and no significant difference at the 95% confidence level was observed. Other profitable features, such as a low reagent consumption of 7.3 microg DPD per determination; a linear response ranging from 0.1 up to 3.0 m IO(3)(-), a relative standard deviation of 0.9% (n=11) for samples containing 0.5 m IO(3)(-), a detection limit of 17 microg L(-1) IO(3)(-), a sampling throughput of 117 determination per hour, and a waste generation 600 microL per determination, were also achieved.

A multicommuted stop-flow system employing LEDs-based photometer for the sequential determination of anionic and cationic surfactants in water.

It has been developed an automatic stop-flow procedure for sequential photometric determination of anionic and cationic surfactants in a same sample of water. The flow system was based on multicommutation process that was designed employing two solenoid micro-pumps and six solenoid pinch valves, which under microcomputer control carry out fluid propelling and reagent solutions handling. A homemade photometer using a photodiode as detector and two light emitting diodes (LEDs) with emission at 470 nm (blue) and 650 nm (red) as radiation sources, which was tailored to allow the determination of anionic and cationic surfactants in waters. The procedure for anionic surfactant determination was based on the substitution reaction of methyl orange (MO) by the anionic surfactant sodium dodecylbenzene sulfonate (DBS) to form an ion-pair with the cetyl pyridine chloride (CPC). Features such as a linear response ranging from 0.35 to 10.5 mg L(-1) DBS (R=0.999), a detection limit of 0.06 mg L(-1) DBS and a relative standard deviation of 0.6% (n=11) were achieved. For cationic surfactant determination, the procedure was based on the ternary complex formation between cationic surfactant, Fe(III) and chromazurol S (CAS) using CPC as reference standard solution. A linear response range between 0.34 and 10.2 mg L(-1) CPC (R=0.999), a detection limit of 0.05 mg L(-1) CPC and a relative standard deviation of 0.5% (n=11) were obtained. In both cases, the sampling throughput was 60 determinations per hour. Reagents consumption of 7.8 microg MO, 8.2 microg CPC, 37.2 microg CAS and 21.6 microg Fe(III) per determination were achieved. Analyzing river water samples and applying t-test between the results found and those obtained using reference procedures for both surfactant types provide no significant differences at 95% confidence level.

An automatic falling drop system based on multicommutation process for photometric chlorine determination in bleach.

In this work an automatic photometric procedure for the determination of chlorine in bleach samples employing N,N'-diethyl-p-phenylenediamine (DPD) as chromogenic reagent is described. The procedure was based on a falling drop system where the analyte (Cl(2)) was collected by a DPD solution drop (50 microL) after its delivery from the sample bulk that was previously acidified. The flow system was designed based on the multicommutation process assembling a set of three-way solenoid valves, which under microcomputer control afforded facilities to handle sample and reagent solution in order to control analyte delivering and solution drop generation. The analyte volatilization was improved by coupling online a little heating device. The detection system comprised a green LED (515 nm) and a phototransistor. Aiming to prove the usefulness of the proposed procedure a set of bleach samples was analyzed. Comparing the results with those obtained with reference method no significant difference at 95% confidence level was observed. Other profitable features such as a linear response ranging from 15 up to 100 mgL(-1) Cl(2) (R=0.999); a detection limit of 4.5 mgL(-1) Cl(2) estimated based on the 3 sigma criterion; a relative standard deviation of 2.5% (n=10) using a typical bleach sample containing 25.0 mgL(-1) Cl(2); a consumption of 55 microg of DPD per determination; and a analytical frequency of 20 determinations per hour were also achieved.

Monitoring of the smoking process by multicommutation Fourier transform infrared spectroscopy.

Nicotine was selected as the target molecule for monitoring of the smoking process by multicommutation Fourier Transform Infrared spectroscopy (FTIR). The method involved the use of CHCl3 for on-line extraction of nicotine from tobacco, cigarette filters and tobacco ash from NH4OH alkalinized samples, and absorbance measurement of the characteristic band at 1316 cm(-1) in the stopped-flow mode, by obtaining the peak area in the range between 1334 and 1300 cm(-1). Under the best operational conditions, the procedure developed provided a detection limit of 0.05 mg mL(-1) nicotine, corresponding to 0.5 mg g(-1) in the solid sample, a relative standard deviation less than 2.5%, and a sampling frequency of 12 determinations h(-1). It can be concluded that nicotine migrates in the smoke mainstream towards the filter during the smoking process. The smoking of cigarettes and cigars is different. Nicotine is retained weakly by both tobacco and filter in the case of cigarettes, and strongly by the unburned tobacco in cigars. The incomplete smoking of cigars and cigarettes reduces nicotine intake and thus reduces the additive effect.

Speciation of chromium in natural waters by micropumping multicommutated light emitting diode photometry.

A simple and sensitive multicommutated flow procedure, implemented by employing a homemade light emitting diode (LED) based photometer, has been developed for the determination of chromium (VI) and total chromium in water. The flow system comprised a set of four solenoid micro-pumps, which were assembled to work as fluid propelling and as commutating devices. The core of the detection unit comprised a green LED source, a photodiode and a homemade flow cell of 100mm length and 2mm inner diameter. The photometric procedure for the speciation of chromium in natural waters was based on the reaction of Cr (VI) with 1,5-diphenylcarbazide. Cr (III) was previously oxidized to Cr (VI) and determined as the difference between total Cr and Cr (VI). After carrying out the assays to select the best operational conditions the features of the method included: a linear response ranging from 10 to 200mugl(-1) Cr (III) and Cr (VI) (r=0.999, n=7); limits of detection of 2.05 and 1.0mugl(-1) for Cr (III) and Cr (VI), respectively; a relative standard deviation lower than 2.0% (n=20) for a typical solution containing 50mugl(-1) Cr; a sampling throughput of 67 and 105 determinations per hour for total Cr and Cr (VI), respectively, and recovery values within the range of 93-108% for spiked concentrations of the order of 50mugl(-1).

A full automatic device for sampling small solution volumes in photometric titration procedure based on multicommuted flow system.

In this work, an automatic device to deliver titrant solution into a titration chamber with the ability to determine the dispensed volume of solution, with good precision independent of both elapsed time and flow rate, is proposed. A glass tube maintained at the vertical position was employed as a container for the titrant solution. Electronic devices were coupled to the glass tube in order to control its filling with titrant solution, as well as the stepwise solution delivering into the titration chamber. The detection of the titration end point was performed employing a photometer designed using a green LED (lambda=545 nm) and a phototransistor. The titration flow system comprised three-way solenoid valves, which were assembled to allow that the steps comprising the solution container loading and the titration run were carried out automatically. The device for the solution volume determination was designed employing an infrared LED (lambda=930 nm) and a photodiode. When solution volume delivered from proposed device was within the range of 5 to 105 mul, a linear relationship (R = 0.999) between the delivered volumes and the generated potential difference was achieved. The usefulness of the proposed device was proved performing photometric titration of hydrochloric acid solution with a standardized sodium hydroxide solution and using phenolphthalein as an external indicator. The achieved results presented relative standard deviation of 1.5%.

Multicommuted flow system employing pinch solenoid valves and micro-pumps. Spectrophotometric determination of paracetamol in pharmaceutical formulations.

A multicommuted spectrophotometric flow-based procedure for the determination of paracetamol in pharmaceutical formulations is proposed. The method is based on the reaction of paracetamol with sodium hypochlorite forming N-acetyl-p-benzoquinoneimine, which reacts with sodium salicylate in alkaline medium producing a blue indophenol dye that was measured at 640nm. The flow system was designed employing four pinch solenoid valves and two solenoid micro-pumps, which were assembled aiming to obtain a compact module, resulting in minimization of reagents consumption and waste generation. Aiming to prove the usefulness of flow system an analytical procedure for paracetamol determination in pharmaceutical formulations was developed. To allow accuracy assessment samples were also analyzed using the AOAC reference method. Applying the paired t-test between results no significant difference at the 95% confidence level was observed. Other profitable features such as a linear response ranging from 5.0 to 125.0mgl(-1) (R=0.9992, n=7), a sampling rate of 60 determinations per hour, a detection limit of 0.4mgl(-1) paracetamol, a relative standard deviation of 1.5% (n=11) for a typical sample solution containing 25.0mgl(-1) paracetamol, reagent consumption of 1.28mg sodium hypochlorite and 6.4mg sodium salicylate per determination were also achieved.

An automatic flow injection analysis procedure for photometric determination of ethanol in red wine without using a chromogenic reagent.

An automatic reagentless photometric procedure for the determination of ethanol in red wine is described. The procedure was based on a falling drop system that was implemented by employing a flow injection analysis manifold. The detection system comprised an infrared LED and a phototransistor. The experimental arrangement was designed to ensure that the wine drop grew between these devices, thus causing a decrease in the intensity of the radiation beam coming from the LED. Since ethanol content affected the size of the wine drop this feature was exploited to develop an analytical procedure for the photometric determination of ethanol in red wine without using a chromogenic reagent. In an attempt to prove the usefulness of the proposed procedure, a set of red wines were analysed. No significant difference between our results and those obtained with a reference method was observed at the 95% confidence level. Other advantages of our method were a linear response ranging from 0.17 up to 5.14 mol L(-1) (1.0 up to 30.0%) ethanol (R = 0.999); a limit of detection of 0.05 mol L(-1) (0.3%) ethanol; a relative standard deviation of 2.5% (n = 10) using typical wine sample containing 2.14 mol L(-1) (12.5%) ethanol; and a sampling rate of 50 determinations per hour.

Evaluation of a multicommuted flow system for photometric environmental measurements.

A portable flow analysis instrument is described for in situ photometric measurements. This system is based on light-emitting diodes (LEDs) and a photodiode detector, coupled to a multipumping flow system. The whole equipment presents dimensions of 25 cm x 22 cm x 10 cm, weighs circa 3 kg, and costs 650 euro. System performance was evaluated for different chemistries without changing hardware configuration for determinations of (i) Fe(3+) with SCN(-), (ii) iodometric nitrite determination, (iii) phenol with sodium nitroprusside, and (iv) 1-naphthol-N-methylcarbamate (carbaryl) with p-aminophenol. The detection limits were estimated as 22, 60, 25, and 60 ng mL (-1) for iron, nitrite, phenol, and carbaryl at the 99.7% confidence level with RSD of 2.3, 1.0, 1.8, and 0.8%, respectively. Reagent and waste volumes were lower than those obtained by flow systems with continuous reagent addition. Sampling rates of 100, 110, 65, and 72 determinations per hour were achieved for iron, nitrite, phenol, and carbaryl determinations.

Instrumentation and automated photometric titration procedure for total acidity determination in red wine employing a multicommuted flow system.

An automated procedure for photometric titration of red wine and associated instrumentation is described. The procedure was based on the flow-batch approach implemented employing multicommutation. The photometric detection was carried out using a homemade LED-based photometer. The mixing device, LED, and photodetector were attached to the titration chamber in order to form a compact and small-sized unit. The flow system comprised an automatic injector and three-way solenoid valves, which were controlled by a microcomputer through an electronic interface card. The software, written in Quick BASIC 4.5, was designed with abilities to accomplish all steps of the titration procedure including data acquisition and real-time processing to decide about the course of titration in the following step and so forth, until the titration endpoint was reached. The usefulness of the proposed titration system was demonstrated by analyzing red wine samples. When results were compared with those obtained using the AOAC reference method, no significant difference was observed at the 95% confidence level. A relative standard deviation of ca 2% (n=9) was obtained when processing a typical red wine sample containing 7.3 gl-1 total acidity expressed as tartaric acid.